The present invention generally relates to electrophotography and more particularly, to an electrophotographic copying apparatus and control thereof.
Generally, an electrophotographic copying apparatus is provided with a photoreceptive drum having a photosensitive or photoreceptor layer formed on the peripheral outer surface thereof and rotatably disposed so as to be driven in a predetermined direction, and processing devices such as a corona charger for uniformly charging the photosensitive layer, a developing device for developing an electrostatic latent image formed on the photosensitive layer into a visible toner image by feeding toner thereonto, a transfer charger for transferring the toner image formed on the photosensitive layer onto a copy paper sheet, a separating charger for separating the copy paper sheet attracted onto the photosensitive layer therefrom, and a charge erasing device for erasing charge remaining on the photosensitive layer, etc., which are sequentially disposed around the photoreceptive drum for carrying out the copying operation. Moreover, a motor for driving the photoreceptive drum for rotation, and the corona charger, developing device, transfer charger, separating charger and charge erasing device, etc. are respectively connected to corresponding responding power sources for energization at separate timings.
More specifically, in the conventional electrophotographic copying apparatus, the devices as described above are arranged in a manner as illustrated, for example, in FIG. 1.
In the known arrangement of FIG. 1, respective high voltage sources HV1, HV2, HV3 and HV4 for feeding power to the corona charger 3, transfer charger 5, separating charger 6, and developing sleeve 4 which are provided in the vicinity of the photoreceptive drum 1, a circuit 12 for controlling the motor M, and a power source 11 for feeding power to the charge erasing device 2 are respectively controlled by HV1 signal, HV2 signal, HV3 signal branched from HV2 signal, HV4 signal, motor signal and Er signal which are generated by a control means CPU (central processing unit).
The output timings of the above respective signals are as shown in a timing chart of FIG. 2. More specifically, for starting the copying operation, the power source HV4 for the developing device 4 is actuated simultaneously with the starting of the motor M. Taking account of inertia inherent in the motor M, said motor M starts rotation after rising of the developing bias voltage. By energizing the developing bias voltage before rotation of the motor, toner is prevented from adhering onto the photosensitive layer 1a of the photoreceptive drum 1. Thereafter, the other high voltage sources HV1, HV2, HV3 and the eraser lamp power source 11 are actuated for effecting the copying.
For completion or termination of the copying, the power source HV1 for the corona charger 3 is first suspended. Subsequently, after passing of the copy paper sheet over the transfer charger 5 and separating charger 6, the respective power sources HV2 and HV3 therefor are simultaneously stopped. Then, after completion of charge erasing for the photosensitive layer 1a from the transfer position to the erasing position, the eraser lamp 2 and the motor M are stopped. Since the motor M requires some time before stopping by inertia, the power source HV4 for the developing device 4 is suspended after the motor M has stopped. The purpose for stopping the developing device 4 at the last stage is to prevent toner from adhesion onto photosensitive surface 1a by the residual charge in the similar manner as in the starting of copying operation.
However, in the conventional arrangement as described above, since the timings for energizing and de-energizing the respective loads are different from each other, it is necessary to output respectively different energizing signals therefor, and thus, there has been such a problem that a plurality of output terminals are required for outputting a plurality of signals, thus resulting in a complication of the control circuit.